A. Field of the Invention
The present invention relates to an apparatus and method for determining or laying out a grid of spatially separated lines or points across a relatively large area, and in particular, to an apparatus and method which, with sufficient accuracy, is cost-effective and efficient for such purpose in terms of labor, time, and resources.
B. Problems in the Art
A variety of situations call for determining a grid of spatially separated lines or points across an area. One example is a grid of stakes in the ground for grading or surveying an area of ground. Another example is determining a grid of test locations across an area to be illuminated. The test locations are used to take light intensity and uniformity readings. Two examples are sports lighting and parking light lighting. Specifications or regulations set intensity and uniformity requirements for the area. There is a need to check if a lighting design actually meets those requirements. A conventional method is to take discrete measurements at uniformly spaced apart test points throughout the area.
A number of other applications for determining a grid of points throughout an area exist. However, the ability to cost-effectively and efficiently determine the grid and mark the points of such a grid, with a sufficient relatively high accuracy, is neither trivial nor easy to accomplish, especially for relatively large areas such as construction sites, sports fields, and parking lots.
A long-used, and still used, economical technique used for laying out test grids to check illumination levels across an area is tape measures. Open reel tape measures available from a variety of manufacturers can extend substantial distances (for example, several hundreds of feet). The equipment is portable and inexpensive. However, it is difficult to obtain high accuracy. Laying a long flexible tape along the ground may not result in a straight line, even when the tape is pulled taut. Wind, other forces or disturbances, undulations, or objects can affect accuracy. It is difficult for the human eye to verify a straight line. One attempted solution for large areas is to use three to four long tapes and geometric principles to check if a tape is in a straight line along the ground. As can be appreciated, however, this takes well-trained and experienced workers (normally more than two) and is relatively slow. It still is difficult to maintain high accuracy, especially outside in a windy environment. Checking and re-checking by repeated measurements with multiple long tapes is tedious and also subject to human error. As can be further appreciated, analogous issues exist with any application that desires a grid of accurately spaced apart locations to be identified across a relatively wide area.
But accuracy is critical in many of these applications. Consider, for example, laying out a grading pattern for a construction site. A grid of stakes is laid out correlated to a precise grading plan to contour to top of the ground for controlling water runoff. If the grid locations are not accurate, the grading plan can be erroneously applied to the ground and result in water runoff problems that cannot be reversible after construction on the site. Similarly, a grid of surveying stakes must accurately be laid out on a construction site. A building plan is correlated to the surveying points in the grid. If the grid points are inaccurate, architectural plans to the area may be inaccurately designed or applied. This could be expensive to correct or change.
Consider the case of sports lighting. Standards of uniformity and intensity across the field are normally imposed. See, e.g., the IESNA Lighting Manual (2000 9th Edition) for information on uniformity and intensity standards for various sports and fields. The lighting designer, many times with the help of a computer program, selects the number and type of lights to meet the standards that are applicable for a field. The lighting company or installer many times has to demonstrate those standards have been met. A grid of test locations is set out in the field and light uniformity and intensity measurements obtained for those test locations. If the grid of test points is inaccurately laid out, it may not validate that the company or installer has met the requirements and could subject it to expensive penalties or additional work. Conversely, results taken at erroneous test points may falsely indicate a problem with the design or installation, causing the company or installer to needlessly, expensively, and erroneously re-aim the fixtures.
Use of measuring tapes uses cheap and easily portable tools, but the risk of error in laying out such grids leaves much room for improvement. Land survey equipment could be used, but it is expensive and requires highly trained and qualified technicians to operate. For example, laser transits are very accurate, but costly and usually require more than one trained operator. They are also relatively slow to use. They must also be calibrated and handled carefully.
GPS and other similar geographic location technology has evolved quickly in the past decades. The cost of hand-held units is not cheap, but has come down in recent years. However, they remain relatively expensive to obtain high accuracy. Also, to determine and mark a number of discrete test points across a relatively large area, such methods are relatively slow.
It can therefore be seen that there is room for improvement in the art for tools and methods of laying out grids of points across a relatively large area that is relatively easy to implement, inexpensive, and quick but achieves relatively high accuracy for a variety of situations, including out-of-doors.